1. Field of the Invention
The present invention relates to a metal-insulator-metal (MIM) capacitor structure and a method for making the same. In particular, the present invention relates to a metal-insulator-metal (MIM) capacitor structure and a method for making the same with a better dielectric layer thickness.
2. Description of the Prior Art
In the semiconductor manufacturing process, the metal-insulator-metal (MIM) capacitor structures made of metal layer/insulator layer/metal layer composite structure have been widely used in the design of the ultra large scale integration (ULSI) because such metal capacitors have lower electrical resistance, smaller parasitic capacitance and no induced voltage shift, so most metal capacitors are made of the metal-insulator-metal structure.
Structurally speaking, the metal-insulator-metal (MIM) capacitor includes a capacitance insulator layer, such as a dielectric layer, disposed between the lower electrode plate and the upper electrode plate. Generally, the metal-insulator-metal (MIM) capacitor occupies a great deal of space on the chip. In order to increase the capacitance integration and to lower the cost, the metal-insulator-metal (MIM) capacitor is supposed to move toward higher capacitance density to enhance the circuit density. One of the possible fashions to increase the capacitance density of the metal-insulator-metal (MIM) capacitor is to decrease the thickness of the dielectric layer. Nevertheless, such solution may likely trigger another problem, such as unacceptably high leak current.
U.S. Pat. No. 6,699,749 discloses a method for making a metal-insulator-metal capacitor. The dielectric layer serving as the capacitance insulator layer may be also used as the etching-stop layer to define the upper electrode plate during the process. The dielectric layer must be thick enough because the dielectric layer serving as the etching-stop layer will be inevitably damaged by the etching and the thickness of the dielectric layer decreases. This scenario obviously goes against what is originally needed.
U.S. Pat. No. 6,730,573 also discloses a method for making a metal-insulator-metal capacitor. A copper layer is used as the etching-stop layer, and all the copper layers which include the metal electrodes and the metal wires for use in the MIM capacitor structure are exposed after etching is completed. Afterwards, a thin barrier layer is disposed on all the exposed copper layers. The material of the barrier layer is selected from Ta, Al, W, TaN and TiN. Because a barrier layer is disposed on all the copper regions, the copper regions serving as conductive wires would have much higher electrical resistance and have adverse effect on the circuit performance.
Therefore, a novel metal-insulator-metal (MIM) capacitor structure and a method for making the same are needed. Such novel metal-insulator-metal (MIM) capacitor structure should have better dielectric layer thickness and maintain a lower electric resistance of the circuits.